Conventional flow cytometry generally uses single-photon excitation of fluorescence from cells or other particles. By labeling cells with multiple dyes, and by using size measurements via the elastically scattered excitation light, multiple-parameter measurements can be made. The tremendous power of this technique has made it the standard way to quantitate fluorescence in cells. For multiple-dye, multi-wavelength analysis, multiple excitation sources (i.e. lasers) may be required. In light of this arrangement, the layout of such devices can be complex. The complexity of standard flow cytometry also arises from the strict requirements on the fluid flow system, which is designed to guarantee that a single cell is excited at a time. This is typically accomplished using sheath flow by hydrodynamic focusing to produce a linear stream of isolated cells, in conjunction with an elliptically focused excitation laser spot to ensure each cell is excited at the same rate.
The strict requirements and complexity of conventional flow cytometers put limits on their applications, despite of the fact that they are indispensable tools in biological studies. According to the present invention, a novel multiphoton flow cytometer is provided that has a single laser source for excitation of multiple dyes and does not require sheath flow conditions. Thus, the multiphoton flow cytometer not only has a simple configuration, but also opens up a wide range of new applications, such as virus detection and in vivo measurements.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.